Control arrangement for self-closing control rod latches

ABSTRACT

Control arrangement for a nuclear reactor non-scramming control rod drive of the magnetic jack type having a self-closing latch for preventing dropping of the rod in the event of loss of electrical power to the associated solenoids. The solenoid which actuates the self-closing latch is connected electrically in series with a solenoid which actuates a moveable gripper and the two are controlled as one. The two magnetic circuits associated therewith are designed to provide an overlap in operation which avoids the possibility of a dropped rod.

FIPB-E UIlllEfl Slates Patent Ruoss CONTROL ARRANGEMENT FOR SELF-CLOSINGCONTROL ROD LATCHES Inventor: Christian William Ruoss, Enfield,

Conn.

Assignee: Combustion Engineering Inc.,

Windsor, Conn.

Filed: Dec. 23, 1971 Appl. No.: 211,445

US. Cl 226/59, 226/163, 226/145, 226/150, 310/14 Int. Cl B6511 17/36Field of Search 226/59, 162, 112 226/163, 164, 165, 166, 52, 54,145,146, 147, 149, 150, 144; 214/27; 176/36 R;

References Cited UNlTED STATES PATENTS 12/1971 Behmke 226/54 Oct. 16,1973 3,480,807 11/1969 Downs et al. 310/12 3,572,161 3/1971Lichtenberger et al 176/36 R 3,124,513 3/1964 l-lawke et a1. 176/36 RPrimary Examiner-Allen N. Knowles Attorney-Eldon l-l. Luther et al.

[5 7] ABSTRACT Control arrangement for a nuclear reactor nonscrammingcontrol rod drive of the magnetic jack type having a self-closing latchfor preventing dropping of the rod in the event of loss of electricalpower to the associated solenoids. The solenoid which actuates theself-closing latch is connected electrically in series with a solenoidwhich actuates a moveable gripper and the two are controlled as one. Thetwo magnetic circuits associated therewith are designed to provide anoverlap in operation which avoids the possibility of a dropped rod.

7 Claims, 3 Drawing Figures mminum 16 um 3.765585 sum 10F 2 FIG. I

PATENIEUBEI 151915 sum I? [If 2 MASTER TIMER CONTROL ARRANGEMENT FORSELF-CLOSING CONTROL ROD LATCHES BACKGROUND OF THE INVENTION In amagnetic jacking type control rod drive, the control rod is movedthrough a plurality of stepping actions. Electromagnetic coils surroundthe control rod housing and are sequentially operated to perform anumber of lifting or lowering steps. Certain coils will energize gripperor latch assemblies which grippingly engage with axially spaced grooveson a control rod extension. Other coils will operate to lift or lower atleast one of the gripper or latch assemblies a short distance. Anothergripper may be engaged to hold the control rod in this position so thatthe first gripper may be disengaged and returned to a starting positionin preparation for gripping and raising or lowering another step. Inscramming type rods these grippers are arranged so as to disengage thecontrol rod extension on loss of power thereby permitting the reactor tobe scrammed by lowering the control rod by gravity even though power isnot available to the jacking means. This is accomplished by letting thecontrol rod fall under the influence of gravity.

Some control rods, particularly those of the scramming type, employanti-ejection latches which prevent the rod from being ejected from thereactor in the event a power failure disengages the conventionalgrippers and a condition of overpressure occurs within the reactor. Suchan anti-ejection latch is typified by that disclosed in German Pat. No.1,206,102 issued June 16, 1966 to Franz Schreiber. This type of latch iseffective to prevent rod ejection but provides little or no resistanceto a free fall of the control rod so thatthe reactor may readily bescrammed during an emergency.

Another type of control rod, that of the nonscramming type, iselectromagnetically stepped in a manner similar to that of the scrammingtype of control rod. The non-scramming type of control rod is generallyused in connection with one or part length control rods used to controllocal reactivity. Such rods are controlled separately from the maincontrol rods and generally contain the neutron poison in the lowerportion only of the rod, with the poison portion of the rod normallypositioned in the vicinity of the local activity which it is desired tocontrol. If these rods were allowed to trip or scram upon the loss ofelectricity, the rod would drop to the bottom of the reactor and thepoison portion would be removed from the region of the local reactivityand a non-poison portion of the rod would take its place in theaforementioned area of reactivity. This would increase the reactivity ofthe reactor just at a time when every effort is being made to reduce thereactivity. Therefore, it is necessary to provide such a non-scrammingrod with a gripper or latch which will prevent movement of the controlrod in either direction in the event of an electrical failure or a scramsituation. Such a gripper is normally designed to be self-closing togrippingly engage the rod in the rod in the event of loss of power. Onesuch self-closing gripper arrangement which successfully prevents a partlength control rod from dropping in the event of a power failure is thatdepicted and described in the application of Harold V. Lichtenberger andChristian W. Ruoss for Self-Closing Control Rod Grippers Ser. No. 211205 filed Dec. 23, 1971. The above-mentioned application describes aself-closing gripper having a geometry such that its linkage forms anovercenter toggle arrangement which will prevent the gripper or latchfrom acting as a ratchet and positively locks it in position upon theloss of electricity.

Conventionally each of the electromagnetic coils which actuate and movethe several latches will be supplied with electricity from sources whichare separate and are individually switched or controlled. A master timeror controller provides the requisite switch to each power sourceassociated with a particular coil.

SUMMARY OF THE INVENTION This invention relates to a control arrangementfor operating the self-closing latch associated with a nonscramming typeof control rod in a nuclear reactor. The electromagnet which serves toactuate the self-closing latch is connected electrically in series withan electromagnet which actuates a rod moving latch into and out ofengagement with the control rod. By connecting the two electromagnetselectrically in series, a power supply heretofore used may be eliminatedand the power switching operating is simplified. The above mentionedconnection of electromagnets will result in the required steppingoperation of the magnetic jacking unit and is preferred because of theresulting safety afforded. The self-closing latch is normally ingripping engagement with the rod and requires energization of itsassociated electromagnet for releasing said latch from engagement, whilethe rod moving latch is normally not in gripping engagement with the rodand requires energization of its associated electromagnet to bring itinto gripping engagement. For this reason connecting these twoelectromagnets in series results in one or the other of the latchesalways being in gripping engagement with the rod, even in the event ofelectrical failure.

Additionally the magnetic circuits associated with each of theelectromagnets connected in series may be structured to provide a shortoverlap in the actuation of the associated latches such that there is notime when neither latch engages the rod and there is a brief time whenboth latches engage the rod. This structuring of the magnetic circuitsensures that the rod will always be grippingly engaged even in the eventof electrical failure and further allows actuation or release of bothlatches to be effected with but a single change of voltage applied tothe series connected circuit.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a side elevation, partiallyin section, and with parts broken away of the self-closing latch shownin gripping relation with a control rod together with the jackingmechanism for the rod.

FIG. 2 is a schematic diagram showing the electrical arrangement of theseveral solenoids and particularly the series connection of theself-closing latch actuating solenoid with the rod moving latchactuating solenoid.

FIG. 3 is a time plot of the current in the above mentioned circuithaving said solenoids connected in series and showing the sequence oflatch operation associated therewith.

DESCRIPTION OF THE PREFERRED EMBODIMENT This invention is shown inconnection with a control rod drive including self-closing rod latchessimilar to that shown and claimed in the application of Llchtenbergerand Ruoss earlier mentioned to which reference may be made for furtherdetails. In the presently preferred embodiment shown in the drawings, acasing or support in the form of an air-tight tube is secured inair-tight relation at the lower end to a removable head 11 of thenuclear reactor vessel 13 and is closed at the upper end to provide ahermetically sealed housing for the control rod and extension 12 whichextends into the reactor vessel and is surrounded by the casing 10. Thecontrol rod is axially moveable in step-by-step motion inside of thecasing 10 by selective actuation of solenoids A, B, C, D, and E arrangedoutside of and around the casing 10. A tubular member shown generally at14 is positioned inside of the casing 10 and surrounding the control rod12. This tubular member 14 is secured at its upper end to the upperportion of the casing 18 and supports all of the internal operatingmechanism for axially moving and holding the control rod. The controlrod extension 12 is linearly axially slidable inside of the tubularmember 14. The tubular member 14 comprises a tube 16, which may be ofmagnetic or nonmagnetic material but is preferably of nonmagneticmaterial, which is threaded into a sleeve 18 of nonmagnetic material atthe lower end and a sleeve 20 of magnetic material at the upper end. Atube 22 similar to tube 16 is threaded into the opposite side of sleeve20 and at its opposite end is threaded into a sleeve 24 of magneticmaterial. The sleeve 24 is forced inward by nut 28 threaded into casing10 to force sleeve 24 down against shoulder 30 in casing 18 and thussupport the entire tubular member 14 fixedly in the casing 10.

The sleeves 18 and 20 are thus secured in fixed position in the casing10. Any suitable locking means such as pins (not shown) may be used toprevent relative turning of the threaded parts. A sleeve 32 which is ofmagnetic material is also secured in fixed position to sleeve 18 of thetubular member 14 intermediate the sleeves l8 and 20. Slidably mountedon the tubular member 14 is an upper rod feeder or moving member 34 ofmagnetic material having one end adjacent to sleeve 20 and the other endadjacent the sleeve 32 so as to be reciprocated between the two sleeveswhich will act as stops for the moving member and limit its linearmovement. A lower feeder or moving member 36 is mounted for axial linearsliding movement on the tubular member 14 and has its upper end adjacentthe lower end of sleeve 32 and its lower end adjacent the upper end ofsleeve 18 for axial movement between the sleeves which will act as stopslimiting such axial linear movement.

When solenoid A is energized moving member 34 is drawn upward towardsleeve 20 by the magnetic flux through sleeve 20 and moving member 34and when solenoid C is energized moving member 34 is drawn downwardtoward sleeve 32 by the magnetic flux through sleeve 32 and the lowerend of moving member 34. Energization of solenoid E will cause movingmem ber 36 to be drawn upward toward sleeve 32 and spring 37 biasesmoving member 36 downwardly to aid its downward movement toward sleeve18 when solenoid E is de-energized. Thus solenoids A, C, and E providethe means for selectively moving members 34 and 36 in either of twoopposite directions between their respective stops.

A latch or gripper 38 is pivotally mounted on moving member 34. Latchoperating sleeve 40 is slidably axially moveable on upper moving member34 and is spring pressed downward by biasing spring 42. A link 44 ispivoted at one end to sleeve 40 and at the other end to the outer end oflatch or gripper 38 so that axial movement of the sleeve 40 relative tomoving member 34 will force the latch or gripper 38 about its pivot andinto gripping relation with the control rod 12 and connect member 34with rod 12 or when moved in the opposite direction withdraw the latchso as to disconnect the moving member 34 from the control rod 12.Control rod 12 is provided with a series of suitable projections 46 withresulting recesses therebetween coacting with the latch 38 to providethe necessary gripping relation. When the latch 38 is in grippingrelation with the rod 12 axial movement of the moving member 34 willcarry the rod 12 along with it to move the rod 12 in the selecteddirection and will limit movement of rod 12 to that of member 34 betweenits cooperating stops. The rod moving member 34 acts as a support forthe link 38 and the pivot 39 connecting the link 38 with its support 34holds the link 38 against linear axial movement with respect to itssupport 34. The lower moving member 36 has a pivoted latch 48, a latchoperating sleeve 50, a sleeve biasing spring 52 and a link 54 connectingthe sleeve 50 and the latch 48 mounted thereon and operating the same asthat described in connection with the upper moving member 34.Energization of solenoid B will draw the sleeve 40 which is of magneticmaterial toward the upper portion of moving member 34 to force the latch38 into gripping relation with the rod 12 and the spring 42 and gravitywill force the sleeve 40 downward to release the gripping action of thelatch 38. Similarly energization of solenoid D will draw the sleeve 50which is of magnetic material upwardly against the action of spring 52to the upper portion of moving member 36 to force the latch 48 intogripping relation with the rod 12 and the spring 52 and gravity willforce the sleeve 50 downward to release the latch 48 from such grippingrelation.

Typically moving member 34 and latch 38 provide the major axial steppingof rod 12 and lower latch 48 is emploeyd to hold the rod while movingmember 34 and latch 38 are repositioned to begin a new step. Accordinglylower moving member 36 will move a much smaller axial distance thanupper moving member 34. The axial travel of moving member 36 is limitedto that necessary to transfer the load of rod 12 between latches 38 and48. Solenoids A and C then are used in the major stepping function andsolenoid E is used in the rod or load transfer function to lift movingmember 36. The downward bias of spring 37 and the weight of rod 12complete the load transfer cycle upon deenergization of solenoid E.

On tube 22, at the upper portion of the tubular member 14, a sleeve 56is secured to tube 22 by being threaded thereon and locked in positionby suitable means such as a pin (not shown) extending through thesleeves 56 and 22. The upper end of the sleeve 56 may receive one ormore latch levers 58, preferably at least three spacedcircumferentially. Each latch 58 is mounted on a pivot 60 in the sleeve56 which together with the tube 22 and the casing 10 act as a supportfor the latch. Latch 58 has a rod gripping portion adjacent one end. Thepivot 60 serves to hold the latch against linear longituidnal movementwith respect to its support. A sleeve 62 which acts as a slider ismounted for linear longitudinal axial movement in the casing 10 and ontube 22. The sleeve 62 is slotted at 64 to receive a link pivoted at oneend at 68 in the slider 62 and pivoted at the other end at 70 at the endof latch 58 adjacent the gripping portion remote from the pivot 60. Abiasing spring 72 mounted in sleeve 24 urges the slider 62 downwardlyaway from the sleeve 24. This downward movement is limited by thecontact of ledge 74 on sleeve 62 with the upper end of sleeve 56 whichacts as a stop for the movement of sleeve 62. The geometry of the link66 and latch 58 is such that when the sleeve 62 is positioned by thestop 76 the links and the latch and their pivots will be positioned soas to form an overcenter toggle. In this position any force applied tothe latch 58 to turn it outward away from this inward gripping positionwith the rod 12 will tend to force the slider or sleeve 62 furtherdownward against the stop 76 and thus securely mechanically lock thelatch 58 in gripping relation with the rod 12 and thus hold the rod 12securely against linear movement in either direction. Gravity willassist in holding this sleeve 62 in its down position and the toggle inits locked position as well as initially urging the sleeve 62 downward.The downward movement of the sleeve 62 will force the gripping portionat the outer free end of the latch 58 into the recesses between theprojections 46 on the rod 12 to provide the necessary gripping action.

A sixth magnet or solenoid, F, is mounted adjacent the upper end ofcasing and when energized serves, through its magnetic flux, to draw thesleeve 62 upwardly against the action of biasing spring 72 and gravityto a position adjacent the lower end of sleeve 24 to thus move the outerend of link 66 upward and withdraw the latch 58 out of gripping relationwith the rod 12. The rod will then be free to be moved in eitherdirecton by the feeding mechanism previously described. Hence wheneverthe solenoid F is demagnetized the latch 58 will be forced by springaction and gravity into gripping relation with the rod 12 so that uponloss of electrical energy the rod 12 will be immediately gripped andheld against axial movement in either direction. The latch 58 and itsactuating mechanism will therefore act as a lock to prevent the controlrod from dropping upon a loss of electricity or a scram condition andwill also act as an antiejection lock.

In order to allow correct operation of the mechanism which steps rod 12,it is desirable that latch 58 be in gripping engagement with the rodwhen no axial motion is intended and that it be disengaged from the rodwhen axial motion is to be effected. conventionally, each of solenoidsA, B, C, D, E, and F has been provided with a separate power sourcewhich is intermediate a main power source and the respective solenoid.These separate intermediate power sources are individually controlled bya central sequencer or timer to control their output voltage.

According to the invention, solenoid F is electrically connected inseries with another solenoid which results in correct stepping operationof rod 12 with singular control of the intermediate power source whichenergizes the two solenoids. It is preferred to connect solenoid B inseries with solenoid F. Generally speaking, during such time as solenoidB is energized and latch 38 is engaging rod 12, solenoid F is alsoenergized to release self-closing latch 58 from rod engagement thuspermitting latch 38 to be moved axially to effect the desired steppingaction. Conversely, when solenoid B is de-energized, solenoid F is alsode-energized and selfclosing latch 58 moves into gripping engagementwith the rod to prevent any significant axial motion. Load transferringlatch 48 is designed to move only small axial distances and may effectthe short axial load transferring movement while latch 58 is actuated toengage or be coupled with rod 12.

As seen in FIG. 2, each of solenoids A, C, D, and E is individuallyconnected by conductors 77 to the outputs of corresponding intermediatepower supplies 78a, 78c, 78d, and 78e respectively. Solenoids B and Fare connected in series across intermediate power supply 78 bf. Each ofthe intermediate power supplies 78a, 78bf, 78c, 78d, and 78e isconnected to master power source 80 which is usually three phase linevoltage. Each of the intermediate power supplies include means (usuallySCRs) for rectifying and switching the three phase line voltage supply.Control signals from a master timer or sequencer 82 of a type well knownin the art are applied to each of the intermediate power supplies tocontrol the amplitude of the DC voltage appearing at their outputterminals 84 and 86. This control varies from one intermediate powersupply to another in a prearranged sequence, a portion of which is to bediscussed later. Generally speaking the control signals serve to switchthe output of each intermediate power supply from a zero voltage stateto a high DC voltage (about volts), this voltage being applied to theelectromagnetic circuits associated with each of the various jackingmechanisms to overcome certain bias forces and actuate the moveablemembers in the magnetic circuit. As the length of a particular air gapis decreased in a magnetic circuit, the magnetomotive force (MMF)required to maintain the gap closed or in a position of decreased lengthis greatly decreased and voltage applied to a solenoid may be reduced toa holding value which provides a decreased MMF. Finally the voltage isreturned to zero whereupon the biasing forces return the moveablemagnetic member to an initial position.

Connecting the actuating solenoid F of self-closing latch 58electrically in series with the actuating solenoid B of rod liftinglatch 38 ensures that an electrical outage or failure in the electricalcircuits associated with any of the several solenoids will not result inunrestrained axial movement of rod 12, but rather, ensures that the rodwill be grippingly engaged. In terminal 86 of power supply 78bf ismaintained at or near ground potential, it is desirable to connectsolenoid F electrically closest thereto as shown in FIG. 2 such that inthe event of an electrical short to ground occurring in the connectionbetween solenoid B and solenoid F, the self-closing latch 58 ismaintained in rod gripping 'engagement.

A further advantage is obtained by designing the magnetic circuitsassociated with latches 38 and 58 such that, when a latch is being movedeither into or out of engagement with the rod, a short period results inwhich both latches are in rod engaging relationship. While this resultmight be accomplished by proper sizing of the springs 42 and 72 relativeto one another to create a stronger engaging bias in latch 58 thandisengaging bias in latch 38, space limitation within casing 10generally precludes use of a spring that would be of sufficient size forlatch 58.

Because both solenoids B and F experience the same current at anymoment, their respective ampere turn products (NI) at any moment havethe same relationship as that of the number of turns in the twosolenoids. The ampere turns of a solenoid represent its MMF at anymoment. The MMF divided by the reluctance (R) of the magnetic circuitrepresents the total flux ((15) in the circuit. If all other aspects ofthe two magnetic circuits associated with solenoids B and F are thesame, the magnetic forces acting upon the moveable members 40 and 62respectively are proportional to the number of conductive turns in thesolenoids. In the preferred embodiment of the invention, the magneticreluctance, R, is substantially the same in the magnetic circuitsassociated with both solenoids B and F and solenoid B is formed of 800conductive turns or coils and solenoid F of 500 turns. The effects ofsuch an arrangement are seen in FIG. 3 wherein the current in the coilsof the two series connected solenoids is plotted against time. Thiscurrent plot results when a control signal from master timer 82 switchesthe DC voltage at the output terminals 84 and $6 of power supply 78 bffrom V. to 150V. at time, t and then reduces the DC voltage to a holdinglevel of about 25 volts at time, and finally returns the voltage to zerovolts at time, t

At t the current and accordingly the MMF in solenoids B and F begins toincrease in the manner characteristic of inductive circuits to the levelor levels required to overcome the biasing force or forces. At t the MMFof solenoid B is sufficient to begin moving latch 38 into engagementwith rod extension 12. As sleeve 40 which actuates latch 38 ismagnetically moved toward member 34 which is presently stationary, aback emfis induced in the electrical circuit producing the down turn incurrent between t, and t At 1 sleeve 40 has reached its limit of traveland stops. The latch 38 is now in gripping engagement with rod 12. Thecurrent continues to build from time until it provides a sufficient MMFin the magnetic circuit of solenoid F to begin moving latch 58 out ofengagement with rod 12. As with solenoid B, when sleeve 56 ismagnetically moved towards sleeve 24 which is stationary, a back emf isinduced causing the down turn in current between t and t At t; sleeve 56has reached its limit of travel and latch 58 no longer engages rod 12.Because there is no longer a back emf, the current builds again after tto its final value which is at least as great as that at i and isdetermined by the electrical impedance of the circuit. At t the voltageis reduced to the holding value and the current decreases to a holdinglevel which continues until t at which time the voltage is switched tozero or some value less that that required by sleeves 40 and 56 tooopose their respective biasing forces. The sequence is repeated at thefrequency of about 1 Hz and the delay between engagement of latch 38 anddisengagement of latch 50 is typically 0.25 seconds.

Means are employed to maintain non-magnetic gaps of predetermined lengthbetween the magnets following energization of the solenoids and movementof the magnet pole pieces into close relationship. These gaps increasethe reluctance which opposes the MMF created by the current in thesolenoids and thereby serve to reduce the magnetic force which acts upona magnet pole piece at a particular MMF. This reduction in the magneticholding force enables gravity and/or biasing means to more rapidlyovercome the holding force and return the moveable magnets to theirnon-energized biased positions. Non-magnetic spacer shims 88 and 90 aretypical of such spacer means. Spacer 88 is affixed to sleeve 40 or 34 tomaintain a gap between sleeve 40 and sleeve 34 when solenoid B isenergized. Spacer 90 is affixed to sleeve 62 or 243 to maintain a gapbetween sleeve 62 and sleeve 24 when solenoid F is energized. In thepreferred embodiment spacer is about 0.060 inches thick in the axialdirection whereas spacer 88 is only about 0.030 inches thick. Theresulting difference in gap lengths aids the difference in the number ofturns between the solenoids associated with latches 38 and 58 tosignificantly reduce that magnetic force holding sleeve 62 relative tothat which holds sleeve 40. This results in latch 58 being returned togripping engagement with rod 12 more rapidly than latch 38 beingdisengaged from the rod when the holding voltage is terminated at t Thisoverlapping engagement during both operations of latches 58 and 38provides additional safety against inadvertant dropping of rod 12.

It will be understood that the embodiment shown and described herein ismerely illustrative and that changes may be made without departing fromthe scope of the invention as claimed.

What is claimed is:

l. in combination, a support; a control rod supported in andlongitudinally, linearly, reciprocable with respect to said support; anelectromagnetic jacking mechanism for reciprocating said rodlongitudinally of said support in opposite directions including at leastone lifting magnet and at least one lifting latch actuating magnet; aself-locking latch fixed on said support against linear movementlongitudinally of said rod including biasing means forcing saidself-locking latch into gripping relation with said rod and includingmeans mechanically locking said rod against movement in either directionwith respect to said support; electromagnetic means for actuating saidself-locking latch, upon energization, to overcome said locking meansand biasing means to move said latch out of gripping relation with saidrod; and means electrically connecting said self-locking latch actuatingelectromagnetic means, with at least one of said lifting and liftinglatch actuating magnets for simultaneous electrical energizationthereof.

2. The apparatus of claim ll wherein said electromagnetic means foractuating said self-locking latch is electrically connected in serieswith said lifting latch actuating electromagnet whereby to effectsimultaneous energization thereof.

3. In combination a support; a control rod supported in andlongitudinally, linearly, reciprocable with respect to said support; anelectromagnetic jacking mechanism for reciprocating said rodlongitudinally of said support in opposite directions including at leastone rod moving means and at least one rod moving latch and its operatingmeans including first biasing means providing a selected biasing forceto said rod moving latch acting to move said latch out of grippingengagement with said rod and first electromagnetic means for producing aforce on said latch when ener gized to overcome the force of said firstbiasing means and actuate said latch into gripping engagement with saidrod; a self-closing latch fixed on said support against linear movementlongitudinally of said rod and having operating means including secondbiasing means providing a selected biasing force to said selfclosinglatch acting to move said latch into gripping engagement with said rodand second electromagnetic means producing a force on said latch whenenergized for overcoming the force of said second bias means to actuatesaid latch out of gripping engagement with said rod; and circuit meansconnecting said first electromagnetic means in series electricalrelationship with said second electromagnetic means to effectsimultaneous energization thereof, the relationship between said firstbiasing means and first electromagnetic means and between said secondbiasing means and second electromagnetic means being selected such thatsaid self-closing latch is actuated to disengage from the rod followingactuation of said rod moving latch into gripping engagement therewithupon energization of said first and second electromagnetic means andsaid rod moving latch disengages from the rod folowing said self-closinglatch moving into gripping engagement therewith upon termination ofenergization of said first and second electromagnetic means.

4. The combination of claim 3 wherein said first electromagnetic meansfor actuating said rod moving latch includes means for effectingactuation of said rod moving latch at a first electrical current in saidseries connected circuit and said second electromagnetic means foractuating said self-closing latch includes means for effecting actuationof said self-closing latch at a second electrical current in said seriesconnected circuit greater than said first current.

5. The combination of claim 4 wherein the biasing forces of said firstand second biasing means respectively are overcome by first and secondmagnetomotive actuating forces respectively and said firstelectromagnetic means include a first solenoid coil having a firstnumber of conductive turns for producing said first magnetomotiveactuating force at said first electrical current and said secondelectromagnetic means include a second solenoid coil having a secondnumber of conductive turns less than said first for producing saidsecond magnetomotive actuating force at said second electrical currentgreater than said first.

6. The combination of claim 5 including means for switchably applying apredetermined voltage across said first and second solenoid coilsconnected in series for providing said first and second currentstherein, the inductance of said coils in said circuit creating a timelag between the attainment of said first and second currentsrespectively.

7. The combination of claim 6 wherein said first electromagnetic meansinclude first and second magnets moveable relative to one another andhaving said rod moving latch connected to one of said magnets; saidsecond electromagnetic means include first and second magnets moveablerelative to one another and having said self-closing latch connected toone of said magnets; each of said first and second magnets associatedwith said first and second electromagnetic means being moveable betweena near and far position relative to one another when saidelectromagnetic means are respectively energized and de-energized, andmeans for maintaining a non-magnetic gap between said magnets in thenear portion which is greater for said magnets associated with saidsecond electromagnetic means than for said magnets associated with saidfirst electromag netic means.

UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION Patent No.3,765585 Dated October 16. 197% Invent r( Christian William Ruoss I Itis certified that error appears in the above-identified patent and thatsaid Letters Patent are hereby corrected as shown below:

Column 2, line 22, change "operating" to --operation-.

Column 7 line 18, change "t" to -t Column 8, line 38, after "means"delete Column 10, line 27, change "portion" to --position-.

Signed and sealed this 23rd clay of July 1971.

(SEAL) Attest:

MCCOY M. GIBSON, JR. C. MARSHALL DANN Attesting Officer Commissioner ofPatents

1. In combination, a support; a control rod supported in andlongitudinally, linearly, reciprocable with respect to said support; anelectromagnetic jacking mechanism for reciprocating said rodlongitudinally of said support in opposite directions including at leastone lifting magnet and at least one lifting latch actuating magnet; aself-locking latch fixed on said support against linear movementlongitudinally of said rod including biasing means forcing saidself-locking latch into gripping relation with said rod and includingmeans mechanically locking said rod against movement in either directionwith respect to said support; electromagnetic means for actuating saidself-locking latch, upon energization, to overcome said locking meansand biasing means to move said latch out of gripping relation with saidrod; and means electrically connecting said self-locking latch actuatingelectromagNetic means, with at least one of said lifting and liftinglatch actuating magnets for simultaneous electrical energizationthereof.
 2. The apparatus of claim 1 wherein said electromagnetic meansfor actuating said self-locking latch is electrically connected inseries with said lifting latch actuating electromagnet whereby to effectsimultaneous energization thereof.
 3. In combination a support; acontrol rod supported in and longitudinally, linearly, reciprocable withrespect to said support; an electromagnetic jacking mechanism forreciprocating said rod longitudinally of said support in oppositedirections including at least one rod moving means and at least one rodmoving latch and its operating means including first biasing meansproviding a selected biasing force to said rod moving latch acting tomove said latch out of gripping engagement with said rod and firstelectromagnetic means for producing a force on said latch when energizedto overcome the force of said first biasing means and actuate said latchinto gripping engagement with said rod; a self-closing latch fixed onsaid support against linear movement longitudinally of said rod andhaving operating means including second biasing means providing aselected biasing force to said self-closing latch acting to move saidlatch into gripping engagement with said rod and second electromagneticmeans producing a force on said latch when energized for overcoming theforce of said second bias means to actuate said latch out of grippingengagement with said rod; and circuit means connecting said firstelectromagnetic means in series electrical relationship with said secondelectromagnetic means to effect simultaneous energization thereof, therelationship between said first biasing means and first electromagneticmeans and between said second biasing means and second electromagneticmeans being selected such that said self-closing latch is actuated todisengage from the rod following actuation of said rod moving latch intogripping engagement therewith upon energization of said first and secondelectromagnetic means and said rod moving latch disengages from the rodfolowing said self-closing latch moving into gripping engagementtherewith upon termination of energization of said first and secondelectromagnetic means.
 4. The combination of claim 3 wherein said firstelectromagnetic means for actuating said rod moving latch includes meansfor effecting actuation of said rod moving latch at a first electricalcurrent in said series connected circuit and said second electromagneticmeans for actuating said self-closing latch includes means for effectingactuation of said self-closing latch at a second electrical current insaid series connected circuit greater than said first current.
 5. Thecombination of claim 4 wherein the biasing forces of said first andsecond biasing means respectively are overcome by first and secondmagnetomotive actuating forces respectively and said firstelectromagnetic means include a first solenoid coil having a firstnumber of conductive turns for producing said first magnetomotiveactuating force at said first electrical current and said secondelectromagnetic means include a second solenoid coil having a secondnumber of conductive turns less than said first for producing saidsecond magnetomotive actuating force at said second electrical currentgreater than said first.
 6. The combination of claim 5 including meansfor switchably applying a predetermined voltage across said first andsecond solenoid coils connected in series for providing said first andsecond currents therein, the inductance of said coils in said circuitcreating a time lag between the attainment of said first and secondcurrents respectively.
 7. The combination of claim 6 wherein said firstelectromagnetic means include first and second magnets moveable relativeto one another and having said rod moving latch connected to one of saidmagnets; said second electromagnetic means include first and secondmagnets mOveable relative to one another and having said self-closinglatch connected to one of said magnets; each of said first and secondmagnets associated with said first and second electromagnetic meansbeing moveable between a near and far position relative to one anotherwhen said electromagnetic means are respectively energized andde-energized, and means for maintaining a non-magnetic gap between saidmagnets in the near portion which is greater for said magnets associatedwith said second electromagnetic means than for said magnets associatedwith said first electromagnetic means.